Root rot of houseplants
Houseplants infected by a root rot often appear wilted and fail to recover after watering. Root rot also causes the lower leaves to yellow or drop. Houseplants which are most often infected include pothos, African violet, begonia, pepperomia, dieffenbachia, and Chinese evergreen. Most root rots are caused by various species of soil-inhabiting fungi, which require cool, moist soils in order to grow and multiply. Conditions which keep the soil moist, such as overwatering, poor soil drainage, inadequate light, and crowding of plants, favor the development of root rot.
Root rot fungi first enter the plant through small feeder roots. If environmental conditions are favorable for disease development, the fungus can spread through most of the root system within 7-10 days, causing death of the plant. Infected roots become brown and mushy due to extensive tissue decay, whereas healthy roots are cream to white colored and firm. Infected roots no longer function properly, causing a reduction in water and nutrient absorption. This shortage within the plant results in poor growth, wilting, yellowing of lower leaves, and premature leaf drop. These general symptoms are often accompanied by other host specific symptoms. For example, pothos leaves turn bright yellow and wilt from the base outward. Pothos leaves may also be reduced in size. On African violets and begonias, lower leaves often appear water-soaked and wilted or weak. Stem rot may also develop, producing water-soaked or blackened areas on the stem near the soil line.
Prevention is the best line of defense against root rot. Since root rot fungi are in the soil, use pasteurized disease-free soil. Do not overwater plants and always use porous soil mixes and containers that provide proper water drainage. In fact, overwatering is the most common problem which leads to the development of root rot.
By the time symptoms appear, it is often too late to save the plant. If you are seeing foliar symptoms of root rot, examine the roots. If root rot is not extensive, repotting in pasteurized soil may rejuvenate some plants. During the process of repotting, prune decayed roots and provide proper soil drainage. Do not reuse infected soil. Pots should be disinfected by soaking in a 10% bleach solution (1 part bleach to 9 parts water) for 30 minutes. Drenching the soil with a fungicide such as thiophanate-methyl (Cleary's 3336) may help control some species of fungi. However, chemicals are only effective if root rot is not extensive and environmental conditions are improved. Control is not possible if root rot is extensive and infected plants should be discarded.
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Revised by Chad Behrendt and Crystal Floyd 2000